Field of the invention
[0001] The invention relates to radio modems comprising a circuit board, a receiver, a transmitter,
and an antenna or a high frequency connector for an antenna assembled on the circuit
board.
Background art
[0002] Most radio modems for cellular systems known in prior art are external devices. An
alternative to an external radio modem is a modem that is an internal card, such as
a PCMCIA card.
[0003] In contrast to radio modems for cellular systems, there are many WLAN or Bluetooth
radio modems that have a compact form, usually the form of a "stick", and that are
connectable to a computer via a USB interface. These devices are adequate for radio
communication over a very small distance only and therefore apt mostly for indoor
use only.
[0004] It remains a task underlying the invention to improve a radio modem for a cellular
system that could be used with a computer and that is external to it. The radio modem
should be suitable for use in a cellular network, such as in a GSM, CDMA, or UMTS
cellular network.
Summary of the invention
[0005] This objective can be achieved as set out in the independent claim.
[0006] The dependent claims describe various advantageous embodiments of the invention.
Advantages of the invention
[0007] If a radio modem that comprises a circuit board, a receiver, a transmitter, and an
antenna or a high frequency connector for an antenna assembled on the circuit board,
has an elongated form so that a connector for connecting the radio modem to a computer
forms one end, and if the antenna, the high frequency connector, or the receiver is
located closer to another end of the radio modem than to the first end, the adverse
effect of interference on the receive path caused by electromagnetic waves from the
computer can be reduced.
[0008] If the radio modem further comprises at least one buffer capacitor physically located
between the connector and the transmitter, the peak power output of the transmitter
can be increased.
[0009] If the radio modem comprises a USB connector, radio modem can be connected to a computer
via an USB port of the computer. This is particularly advantageous, since a USB port
is currently a de-facto standard and can be found in practically any computer.
[0010] By adding connecting means for a headset and/or a microphone to the radio modem,
the connecting means located between the connector and the antenna, the high frequency
connector, or the receiver, the distance of these components sensitive for electromagnetic
disturbances from the computer can be increased in a meaningful way.
[0011] If said connecting means is a Bluetooth chip, the comfort of use may be increased
since a headset and/or a microphone can be used wirelessly.
[0012] If the radio modem further comprises receiving means for a smart card, located between
the connector and the antenna, the high frequency connector or the receiver, the distance
of these components sensitive for electromagnetic disturbances from the computer can
be further increased still avoiding enlarging the size of the radio modem in a redundant
way.
Detailed description
[0013] The maximum transmitting power of a WLAN or Bluetooth transmitter is less than that
of a transmitter suitable for use in a cellular network. In GSM, for example, it has
been specified that the maximum up-link transmitting power of a transmitter should
be 2 W in a burst. Therefore, the electronic design of a prior art WLAN or Bluetooth
transmitter cannot be directly used.
[0014] A consequence of the high transmission power required is that the radio modem, especially
the transmitter in it, needs much current. The present inventor has estimated the
peak current consumption to be up to 2 A.
[0015] This peak value is much more than the upper limit for an average current intake 500
mA specified in the USB 2.0 specifications, for example, allows. This difference may
become particularly disturbing if the radio modem were used in a multi-slot communication
mode, i.e. that the transmitter would send data in more than one time slots in a burst,
since then the radio modem would exceed the average limit of 500 mA current intake
four-fold for a number of time slots. For GSM networks, multi-slot communication mode
has been defined for the General Packet Radio Service GPRS and for the Enhanced Data
Rates GSM Evolution EDGE, for example.
[0016] The only Figure shows a radio modem 10. The radio modem 10 comprises an antenna 1
that has been arranged directly next to radio module 2 in order to minimize attenuation
in the transmit-receive part. The radio module 2 comprises a radio receiver, a radio
transmitter, and a base band unit.
[0017] The antenna 1 is placed on the other side of the radio modem 10 than the USB connector.
The antenna 1 will thus be located further away from the computer to which the radio
modem 10 is connected. In this way, the degradation of the received radio frequency
signal because of interfering electromagnetic waves from the computer can be minimized.
The USB connector 6 serves for connection to the computer, from which operating current
is received. The USB connector is used for data transfer to and from the computer
too. A USB controller (not shown in Figure) for the radio modem 10 is implemented
of the back side of the circuit board 13.
[0018] The antenna 1 may be a foldable strip that has been embedded in a plastic housing
of the radio modem 10 (omitted from the Figure). Instead of comprising an antenna
1 directly on the Printed Circuit Board PCB 13, the PCB 13 may comprise a high frequency
(HF) connector for the antenna, to which an external antenna may be connected.
[0019] The impedance of the antenna 1 is matched to the PCB 13. The buffer zone 4 consists
of at least one buffer capacitor that enable the peak current of 2 A in a burst. The
middle current intake of the radio module 10 can thus be maintained at 500 mA level
or even less.
[0020] The PCB 13 may further comprise connecting means 3, such as a pair of connectors,
two mechanical slots or a Bluetooth chip, for headset and microphone. Further, the
PCB 13 preferably comprises receiving means 5, such as a slot, for a smart card, such
as a Subscriber Identity Module or User Identity Module, the smart card comprising
subscriber data for the cellular network.
[0021] By reserving the means 3 and 5 in the PCB between the radio module 2 and the USB
connector, the distance of the GSM receiver integrated in the radio module 2 can be
increased from the computer, which contributes in eliminating disturbances at the
receiver. The distance between the antenna 1 and the computer is increased too.
[0022] Because the radio module 2 is further away from the computer, the cooling of the
radio modem 10 can be improved. This is an advantage particularly important when the
radio module 2 is used with a high output power, especially when the output power
can be up to 2 W of high frequency power in a burst for one or more time slots.
[0023] Furthermore, by suitably dimensioning the PCB 13 to show an elongated form, an optimal
construction length can be achieved so that the radiation characteristics of the antenna
are essentially improved. For example, when the antenna 1 is used to transmit on a
GSM 900 MHz band, the PCB 13 acts as the main radiating element. In the GSM 1800 MHz
band, the antenna 1 acts as the main radiating element. In both cases the length of
the PCB 13 nevertheless has an large effect on the resulting bandwidth. For example,
for the GSM 900 MHz band, to obtain an optimum bandwidth for the antenna 1 it would
be necessary for the PCB 13 to have a length of 12-13 cm. For GSM 1800 MHz band, the
PCB 13 can be shorter.
1. A radio modem (10), comprising:
- a circuit board (13) further comprising a connector (6) for connecting the radio
modem (10) to a computer;
- a receiver (2) and a transmitter (2);
- an antenna (1) or a high frequency connector for an antenna assembled on the circuit
board (13);
characterized in that:
the radio modem (10) has an elongated form, the connector (6) forming one end (A);
and at least one of the following: the antenna (1), the high frequency connector,
or the receiver (2) is located closer to another end (B) of the radio modem (10) than
to the first end (A).
2. A radio modem (10) according to claim 1, further comprising: at least one buffer capacitor (4) physically located between the connector (6) and
the transmitter (2).
3. A radio modem (10) according to claim 1 or 2, wherein: the connector (6) is a USB connector.
4. A radio modem (10) according to any one of the preceding claims, further comprising: connecting means (3) for a headset and/or a microphone, located between the connector
(6) and the antenna (1), the high frequency connector, or the receiver (2).
5. A radio modem (10) according to claim 4, wherein: said connecting means (3) is a Bluetooth chip.
6. A radio modem (10) according to any one of the preceding claims, further comprising: receiving means (5) for a smart card located between the connector (6) and the antenna
(1), the high frequency connector, or the receiver (2).
7. A radio modem (10) according to any one of the preceding claims, wherein: the receiver (2) and the transmitter (2) are adapted to communicate with a cellular
network.
8. A radio modem (10) according to 7, wherein: said cellular network is a GSM, CDMA, or UMTS network.
9. A radio modem (10) according to any one of the preceding claims, wherein: said antenna (1) is a foldable strip that has been embedded in a plastic housing
of the radio modem (10).